Re: [PATCH v3 net 3/4] dccp/tcp: Update saddr under bhash's lock.

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From:   Kuniyuki Iwashima <kuniyu@amazon.com>
Date:   Fri, 18 Nov 2022 15:57:53 -0800
> From:   Joanne Koong <joannelkoong@gmail.com>
> Date:   Fri, 18 Nov 2022 15:20:20 -0800
> > On Fri, Nov 18, 2022 at 1:00 PM Kuniyuki Iwashima <kuniyu@amazon.com> wrote:
> > >
> > > When we call connect() for a socket bound to a wildcard address, we update
> > > saddr locklessly.  However, it could result in a data race; another thread
> > > iterating over bhash might see a corrupted address.
> > >
> > > Let's update saddr under the bhash bucket's lock.
> > 
> > Thanks for the quick turnaround!
> > 
> > >
> > > Fixes: 3df80d9320bc ("[DCCP]: Introduce DCCPv6")
> > > Fixes: 7c657876b63c ("[DCCP]: Initial implementation")
> > > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> > > Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
> > > ---
> > >  include/net/inet_hashtables.h |  2 +-
> > >  net/dccp/ipv4.c               | 22 +++-----------
> > >  net/dccp/ipv6.c               | 23 +++------------
> > >  net/ipv4/af_inet.c            | 11 +------
> > >  net/ipv4/inet_hashtables.c    | 55 +++++++++++++++++++++++++++++------
> > >  net/ipv4/tcp_ipv4.c           | 20 +++----------
> > >  net/ipv6/tcp_ipv6.c           | 19 ++----------
> > >  7 files changed, 63 insertions(+), 89 deletions(-)
> > >
> > > diff --git a/include/net/inet_hashtables.h b/include/net/inet_hashtables.h
> > > index 3af1e927247d..ba06e8b52264 100644
> > > --- a/include/net/inet_hashtables.h
> > > +++ b/include/net/inet_hashtables.h
> > > @@ -281,7 +281,7 @@ inet_bhash2_addr_any_hashbucket(const struct sock *sk, const struct net *net, in
> > >   * sk_v6_rcv_saddr (ipv6) changes after it has been binded. The socket's
> > >   * rcv_saddr field should already have been updated when this is called.
> > >   */
> > > -int inet_bhash2_update_saddr(struct inet_bind_hashbucket *prev_saddr, struct sock *sk);
> > > +int inet_bhash2_update_saddr(struct sock *sk, void *saddr, int family);
> > >
> > >  void inet_bind_hash(struct sock *sk, struct inet_bind_bucket *tb,
> > >                     struct inet_bind2_bucket *tb2, unsigned short port);
> > > diff --git a/net/dccp/ipv4.c b/net/dccp/ipv4.c
> > > index 40640c26680e..95e376e3b911 100644
> > > --- a/net/dccp/ipv4.c
> > > +++ b/net/dccp/ipv4.c
> > > @@ -45,11 +45,10 @@ static unsigned int dccp_v4_pernet_id __read_mostly;
> > >  int dccp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
> > >  {
> > >         const struct sockaddr_in *usin = (struct sockaddr_in *)uaddr;
> > > -       struct inet_bind_hashbucket *prev_addr_hashbucket = NULL;
> > > -       __be32 daddr, nexthop, prev_sk_rcv_saddr;
> > >         struct inet_sock *inet = inet_sk(sk);
> > >         struct dccp_sock *dp = dccp_sk(sk);
> > >         __be16 orig_sport, orig_dport;
> > > +       __be32 daddr, nexthop;
> > >         struct flowi4 *fl4;
> > >         struct rtable *rt;
> > >         int err;
> > > @@ -91,26 +90,13 @@ int dccp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
> > >                 daddr = fl4->daddr;
> > >
> > >         if (inet->inet_saddr == 0) {
> > > -               if (inet_csk(sk)->icsk_bind2_hash) {
> > > -                       prev_addr_hashbucket =
> > > -                               inet_bhashfn_portaddr(&dccp_hashinfo, sk,
> > > -                                                     sock_net(sk),
> > > -                                                     inet->inet_num);
> > > -                       prev_sk_rcv_saddr = sk->sk_rcv_saddr;
> > > -               }
> > > -               inet->inet_saddr = fl4->saddr;
> > > -       }
> > > -
> > > -       sk_rcv_saddr_set(sk, inet->inet_saddr);
> > > -
> > > -       if (prev_addr_hashbucket) {
> > > -               err = inet_bhash2_update_saddr(prev_addr_hashbucket, sk);
> > > +               err = inet_bhash2_update_saddr(sk,  &fl4->saddr, AF_INET);
> > >                 if (err) {
> > > -                       inet->inet_saddr = 0;
> > > -                       sk_rcv_saddr_set(sk, prev_sk_rcv_saddr);
> > >                         ip_rt_put(rt);
> > >                         return err;
> > >                 }
> > > +       } else {
> > > +               sk_rcv_saddr_set(sk, inet->inet_saddr);
> > >         }
> > >
> > >         inet->inet_dport = usin->sin_port;
> > > diff --git a/net/dccp/ipv6.c b/net/dccp/ipv6.c
> > > index 626166cb6d7e..94c101ed57a9 100644
> > > --- a/net/dccp/ipv6.c
> > > +++ b/net/dccp/ipv6.c
> > > @@ -934,26 +934,11 @@ static int dccp_v6_connect(struct sock *sk, struct sockaddr *uaddr,
> > >         }
> > >
> > >         if (saddr == NULL) {
> > > -               struct inet_bind_hashbucket *prev_addr_hashbucket = NULL;
> > > -               struct in6_addr prev_v6_rcv_saddr;
> > > -
> > > -               if (icsk->icsk_bind2_hash) {
> > > -                       prev_addr_hashbucket = inet_bhashfn_portaddr(&dccp_hashinfo,
> > > -                                                                    sk, sock_net(sk),
> > > -                                                                    inet->inet_num);
> > > -                       prev_v6_rcv_saddr = sk->sk_v6_rcv_saddr;
> > > -               }
> > > -
> > >                 saddr = &fl6.saddr;
> > > -               sk->sk_v6_rcv_saddr = *saddr;
> > > -
> > > -               if (prev_addr_hashbucket) {
> > > -                       err = inet_bhash2_update_saddr(prev_addr_hashbucket, sk);
> > > -                       if (err) {
> > > -                               sk->sk_v6_rcv_saddr = prev_v6_rcv_saddr;
> > > -                               goto failure;
> > > -                       }
> > > -               }
> > > +
> > > +               err = inet_bhash2_update_saddr(sk, saddr, AF_INET6);
> > > +               if (err)
> > > +                       goto failure;
> > >         }
> > >
> > >         /* set the source address */
> > > diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
> > > index 4728087c42a5..0da679411330 100644
> > > --- a/net/ipv4/af_inet.c
> > > +++ b/net/ipv4/af_inet.c
> > > @@ -1230,7 +1230,6 @@ EXPORT_SYMBOL(inet_unregister_protosw);
> > >
> > >  static int inet_sk_reselect_saddr(struct sock *sk)
> > >  {
> > > -       struct inet_bind_hashbucket *prev_addr_hashbucket;
> > >         struct inet_sock *inet = inet_sk(sk);
> > >         __be32 old_saddr = inet->inet_saddr;
> > >         __be32 daddr = inet->inet_daddr;
> > > @@ -1260,16 +1259,8 @@ static int inet_sk_reselect_saddr(struct sock *sk)
> > >                 return 0;
> > >         }
> > >
> > > -       prev_addr_hashbucket =
> > > -               inet_bhashfn_portaddr(tcp_or_dccp_get_hashinfo(sk), sk,
> > > -                                     sock_net(sk), inet->inet_num);
> > > -
> > > -       inet->inet_saddr = inet->inet_rcv_saddr = new_saddr;
> > > -
> > > -       err = inet_bhash2_update_saddr(prev_addr_hashbucket, sk);
> > > +       err = inet_bhash2_update_saddr(sk, &new_saddr, AF_INET);
> > >         if (err) {
> > > -               inet->inet_saddr = old_saddr;
> > > -               inet->inet_rcv_saddr = old_saddr;
> > >                 ip_rt_put(rt);
> > >                 return err;
> > >         }
> > > diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
> > > index d745f962745e..fce0bd62d6b5 100644
> > > --- a/net/ipv4/inet_hashtables.c
> > > +++ b/net/ipv4/inet_hashtables.c
> > > @@ -858,31 +858,65 @@ inet_bhash2_addr_any_hashbucket(const struct sock *sk, const struct net *net, in
> > >         return &hinfo->bhash2[hash & (hinfo->bhash_size - 1)];
> > >  }
> > >
> > > -int inet_bhash2_update_saddr(struct inet_bind_hashbucket *prev_saddr, struct sock *sk)
> > > +static void inet_update_saddr(struct sock *sk, void *saddr, int family)
> > > +{
> > > +       if (family == AF_INET) {
> > > +               inet_sk(sk)->inet_saddr = *(__be32 *)saddr;
> > > +               sk_rcv_saddr_set(sk, inet_sk(sk)->inet_saddr);
> > > +       }
> > > +#if IS_ENABLED(CONFIG_IPV6)
> > > +       else {
> > > +               sk->sk_v6_rcv_saddr = *(struct in6_addr *)saddr;
> > > +       }
> > > +#endif
> > > +}
> > > +
> > > +int inet_bhash2_update_saddr(struct sock *sk, void *saddr, int family)
> > >  {
> > >         struct inet_hashinfo *hinfo = tcp_or_dccp_get_hashinfo(sk);
> > > +       struct inet_bind_hashbucket *head, *head2;
> > >         struct inet_bind2_bucket *tb2, *new_tb2;
> > >         int l3mdev = inet_sk_bound_l3mdev(sk);
> > > -       struct inet_bind_hashbucket *head2;
> > >         int port = inet_sk(sk)->inet_num;
> > >         struct net *net = sock_net(sk);
> > > +       int bhash, err = 0;
> > > +
> > > +       if (!inet_csk(sk)->icsk_bind2_hash) {
> > > +               /* Not bind()ed before. */
> > > +               inet_update_saddr(sk, saddr, family);
> > > +               goto out;
> > > +       }
> > 
> > I think it would be cleaner if this logic were outside
> > bhash2_update_saddr(), since this mutates the sk's address when the
> > socket hasn't been previously bound to bhash2. I think something like
> > this would be clearer:
> > 
> > static int inet_update_saddr(struct sock *sk, void *saddr, int family)
> > {
> >     if (!inet_csk(sk)->icsk_bind2_hash) {
> >       update_sk_saddr(sk, saddr, family)
> >       return 0;
> >     }
> >     return inet_bhash2_update_saddr(sk, saddr, family);
> > }
> > 
> > and then from dccp/tcp_ipv4/6_connect(), we just call
> > inet_update_saddr(). This also "moves" the lower-level implementation
> > details (eg underlying bind tables) to inet_hashtables.c, instead of
> > it being mentioned in the higher dccp_tcp_ipv4/6 layers.
> > 
> > What are your thoughts?
> 
> Sounds good!
> I'll change them like above.
> 
> 
> > 
> > > +
> > > +       bhash = inet_bhashfn(net, port, hinfo->bhash_size);
> > > +       head = &hinfo->bhash[bhash];
> > > +
> > > +       /* If we change saddr locklessly, another thread
> > > +        * iterating over bhash might see corrupted address.
> > > +        */
> > > +       spin_lock_bh(&head->lock);
> > 
> > I don't think we should be acquiring the bhash lock here. I think we
> > only need to acquire it right before we mutate the saddr, and we can
> > release it right after.
> 
> Exactly, will move it down before "__"inet_update_saddr() :)

And I'll move this down after the first inet_bhashfn_portaddr() to
align the same lock semantics with these 3 functions which aquire
the bhash's lock before updating a bhash2 bucket.

  * inet_csk_get_port()
  * __inet_hash_connect()
  * inet_put_port()


> 
> Thank you!
> 
> 
> > >         /* Allocate a bind2 bucket ahead of time to avoid permanently putting
> > >          * the bhash2 table in an inconsistent state if a new tb2 bucket
> > >          * allocation fails.
> > >          */
> > >         new_tb2 = kmem_cache_alloc(hinfo->bind2_bucket_cachep, GFP_ATOMIC);
> > > -       if (!new_tb2)
> > > -               return -ENOMEM;
> > > +       if (!new_tb2) {
> > > +               err = -ENOMEM;
> > > +               goto unlock;
> > > +       }
> > >
> > >         head2 = inet_bhashfn_portaddr(hinfo, sk, net, port);
> > >
> > > -       spin_lock_bh(&prev_saddr->lock);
> > > +       spin_lock(&head2->lock);
> > >         __sk_del_bind2_node(sk);
> > >         inet_bind2_bucket_destroy(hinfo->bind2_bucket_cachep, inet_csk(sk)->icsk_bind2_hash);
> > > -       spin_unlock_bh(&prev_saddr->lock);
> > > +       spin_unlock(&head2->lock);
> > > +
> > > +       inet_update_saddr(sk, saddr, family);
> > >
> > > -       spin_lock_bh(&head2->lock);
> > > +       head2 = inet_bhashfn_portaddr(hinfo, sk, net, port);
> > > +
> > > +       spin_lock(&head2->lock);
> > >         tb2 = inet_bind2_bucket_find(head2, net, port, l3mdev, sk);
> > >         if (!tb2) {
> > >                 tb2 = new_tb2;
> > > @@ -890,12 +924,15 @@ int inet_bhash2_update_saddr(struct inet_bind_hashbucket *prev_saddr, struct soc
> > >         }
> > >         sk_add_bind2_node(sk, &tb2->owners);
> > >         inet_csk(sk)->icsk_bind2_hash = tb2;
> > > -       spin_unlock_bh(&head2->lock);
> > > +       spin_unlock(&head2->lock);
> > >
> > >         if (tb2 != new_tb2)
> > >                 kmem_cache_free(hinfo->bind2_bucket_cachep, new_tb2);
> > >
> > > -       return 0;
> > > +unlock:
> > > +       spin_unlock_bh(&head->lock);
> > > +out:
> > > +       return err;
> > >  }
> > >  EXPORT_SYMBOL_GPL(inet_bhash2_update_saddr);
> > >
> > > diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
> > > index 6a3a732b584d..23dd7e9df2d5 100644
> > > --- a/net/ipv4/tcp_ipv4.c
> > > +++ b/net/ipv4/tcp_ipv4.c
> > > @@ -199,15 +199,14 @@ static int tcp_v4_pre_connect(struct sock *sk, struct sockaddr *uaddr,
> > >  /* This will initiate an outgoing connection. */
> > >  int tcp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
> > >  {
> > > -       struct inet_bind_hashbucket *prev_addr_hashbucket = NULL;
> > >         struct sockaddr_in *usin = (struct sockaddr_in *)uaddr;
> > >         struct inet_timewait_death_row *tcp_death_row;
> > > -       __be32 daddr, nexthop, prev_sk_rcv_saddr;
> > >         struct inet_sock *inet = inet_sk(sk);
> > >         struct tcp_sock *tp = tcp_sk(sk);
> > >         struct ip_options_rcu *inet_opt;
> > >         struct net *net = sock_net(sk);
> > >         __be16 orig_sport, orig_dport;
> > > +       __be32 daddr, nexthop;
> > >         struct flowi4 *fl4;
> > >         struct rtable *rt;
> > >         int err;
> > > @@ -251,24 +250,13 @@ int tcp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
> > >         tcp_death_row = &sock_net(sk)->ipv4.tcp_death_row;
> > >
> > >         if (!inet->inet_saddr) {
> > > -               if (inet_csk(sk)->icsk_bind2_hash) {
> > > -                       prev_addr_hashbucket = inet_bhashfn_portaddr(tcp_death_row->hashinfo,
> > > -                                                                    sk, net, inet->inet_num);
> > > -                       prev_sk_rcv_saddr = sk->sk_rcv_saddr;
> > > -               }
> > > -               inet->inet_saddr = fl4->saddr;
> > > -       }
> > > -
> > > -       sk_rcv_saddr_set(sk, inet->inet_saddr);
> > > -
> > > -       if (prev_addr_hashbucket) {
> > > -               err = inet_bhash2_update_saddr(prev_addr_hashbucket, sk);
> > > +               err = inet_bhash2_update_saddr(sk,  &fl4->saddr, AF_INET);
> > >                 if (err) {
> > > -                       inet->inet_saddr = 0;
> > > -                       sk_rcv_saddr_set(sk, prev_sk_rcv_saddr);
> > >                         ip_rt_put(rt);
> > >                         return err;
> > >                 }
> > > +       } else {
> > > +               sk_rcv_saddr_set(sk, inet->inet_saddr);
> > >         }
> > >
> > >         if (tp->rx_opt.ts_recent_stamp && inet->inet_daddr != daddr) {
> > > diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
> > > index 81b396e5cf79..2f3ca3190d26 100644
> > > --- a/net/ipv6/tcp_ipv6.c
> > > +++ b/net/ipv6/tcp_ipv6.c
> > > @@ -292,24 +292,11 @@ static int tcp_v6_connect(struct sock *sk, struct sockaddr *uaddr,
> > >         tcp_death_row = &sock_net(sk)->ipv4.tcp_death_row;
> > >
> > >         if (!saddr) {
> > > -               struct inet_bind_hashbucket *prev_addr_hashbucket = NULL;
> > > -               struct in6_addr prev_v6_rcv_saddr;
> > > -
> > > -               if (icsk->icsk_bind2_hash) {
> > > -                       prev_addr_hashbucket = inet_bhashfn_portaddr(tcp_death_row->hashinfo,
> > > -                                                                    sk, net, inet->inet_num);
> > > -                       prev_v6_rcv_saddr = sk->sk_v6_rcv_saddr;
> > > -               }
> > >                 saddr = &fl6.saddr;
> > > -               sk->sk_v6_rcv_saddr = *saddr;
> > >
> > > -               if (prev_addr_hashbucket) {
> > > -                       err = inet_bhash2_update_saddr(prev_addr_hashbucket, sk);
> > > -                       if (err) {
> > > -                               sk->sk_v6_rcv_saddr = prev_v6_rcv_saddr;
> > > -                               goto failure;
> > > -                       }
> > > -               }
> > > +               err = inet_bhash2_update_saddr(sk, saddr, AF_INET6);
> > > +               if (err)
> > > +                       goto failure;
> > >         }
> > >
> > >         /* set the source address */
> > > --
> > > 2.30.2